


Relinquish

by Andromeda_Schwarz



Category: Undertale (Video Game)
Genre: Asphyxiation, Biting, Dom Sans, F/M, Growling, Grumpy Sans, Rough Sex, Sans is a smug asshole, Sans is not a Morning Person, Slight Masochism, Sub Undyne, Wall-Slamming, Wrestling, slight Breeding Kink
Language: English
Status: Completed
Published: 2017-04-17
Updated: 2017-04-17
Packaged: 2018-10-19 21:38:52
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,706
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10648566
Author URL: https://archiveofourown.org/users/Andromeda_Schwarz/pseuds/Andromeda_Schwarz
Summary: Sans was never a morning person, he was quite the grouch but he would put up with anything to see Papyrus smile, though once he's gone that irritation is at it's peak and he isn't willing to put up with too much, and Undyne is testing his patience.Though she doesn't really learn her lesson.





	Relinquish

**Author's Note:**

> You guys are probably wondering what exactly the hell this is, I don't blame you, the only reason I even came up with this idea was because I read a story called After the End, which is a Sans/Frisk fic and in one of the chapters where Frisk & Sans is talking his mentions he had sex with Undyne in one of the timelines just to see how it would feel and Frisk deemed this an impossible feat. 
> 
> Once I saw this the idea didn't get out of my head and I had to write this.

It was another day of Papyrus going to Undyne’s to do his training, while they had cooking lessons they also did actual physical training to keep Papyrus’ strength up. As Undyne mentioned Papyrus was actually very strong, but he was just too innocent to be in something like the Royal Guard, maybe it was a bit selfish but Undyne found that she could fine tune her techniques on Papyrus since he was so difficult to beat when he was in a legitimate sparring mode he gave it his all. It was when Papyrus thought things were serious that he held back, he could never seriously harm someone, the intent just wasn’t in his soul, he wasn’t that type of Monster.

Though with this being said Papyrus was still a remarkable fighter and Undyne has praised him on said techniques, so that obviously got back to Sans through Papyrus’ excited summarization of his day, if there was one thing Papyrus loved it was praise and compliments, and he loved the look of approval and pride in Sans’ eyes whenever he heard things like this, honestly Papyrus was kind of addicted to it.

So, it came the day in which Papyrus dragged Sans out of the bed and forcing him to get in something presentable to greet the Captain of the Royal Guard. Papyrus wanted Sans to see him spar and actually witness his greatness in action. Now Sans usually never had an issue being dragged along for Papyrus’ antics but he was _never_ up this early, it was 7 in the _fucking morning_ and this made Sans a very grouchy monster, this further reinforced when Papyrus forced him into something less comfortable than his lazy get-up.

Sans essentially ended up getting in a pair of black jeans with a black T-shirt and denim jacket on top with regular sneakers to finish it off. It wasn’t much but that was the most Papyrus was going to get out of him, it was way too early for Sans to have the proper mindset for his brother’s energetic attitude.

He stepped out of his room with a strained grin, he had to remember not to let his brother see his angry expression, he knew Papyrus was always like this but he couldn’t help the irritation in his soul at his sleep being cut short, not to mention he would have to deal with being around Papyrus AND Undyne, both very loud and energetic people that took some mental preparation to be around for an introvert like Sans.

“SANS! You’re up and you look wonderful! You clean up well!” Sans raised an eye bone at this, he hadn’t even really cleaned up all too much he was just wearing different clothes. Maybe it didn’t take much for him to look that good.

“…yeah yeah i’m up…” Sans let out a loud yawn, the sleep still heavy in his system and he almost squeaked when Papyrus grabbed his arm and forced him to jog to keep up with him as he bolted out of the door, _for fuck sake papyrus!_

Sans wasn’t used to exerting this much physical energy let alone so early!

“Papyrus for fuck sake slow down! I’m not a morning person and you got me up at the ass crack of dawn running through the underground!” Sans was panting heavily and then Papyrus stopped and he practically crashed into his battle body.

“S-sorry brother…I just uhm…r-really wanted to show you how good I am…” Sans felt absolute dread fill his soul and practically recoiled from the force of it, he had never meant to hurt Papyrus by his outburst and he winced from the pain it brought him, here he was being selfish about not getting enough sleep and his brother was busting his ass training to be in the Royal Guard.

“shit sorry paps I didn’t mean to sound so harsh…I’m just…still really tired.” Another yawn left his mouth and he had to stop himself from slumping forward and allowing his skull to crack against Papyrus’ armor. He was _really_ too tired for this…

Sans couldn’t see it but a grin stretched across Papyrus’ face as he had played him like a fiddle. Papyrus knew how much Sans cared for him and knew exactly what to say to get certain reactions out of him. Usually Sans was too smart to fall for stuff like this but Papyrus was the only person who could play Sans like this. Was that manipulative? Yes, but Papyrus found it cute how much his brother tried to please him, it warmed his soul.

Slowing down a bit they quietly walked through the Waterfall, enjoying the pleasant sound of the flowing water and early morning smells the soil brought. The atmosphere was incredibly relaxing and Sans felt like he could fall asleep walking, though he only turned grumpy again when Papyrus turned the corner and they were at Undyne’s house. He could a slight growl make its way up his chest now that he knew he wouldn’t be getting any rest.

Sans jolted when Papyrus gave 3 loud knocks to Undyne’s door and it almost immediately opened afterward, Undyne’s beaming face greeting Papyrus, she was already adorned in her armor and seemed ready to go, but seemed shocked to see Sans there, and also not dressed in his usual get up. He felt mild confusion when her gaze lingered a bit longer than it should.

“HEY PAPYRUS! And Sans surprised to see you here, and so early at that!” She gave him a beaming grin and he tried to return it but his grumpiness was even worse now, there was something about morning people that just angered him even more, he could only stand it with Papyrus. He gave an acknowledging grunt towards her and sauntered off to a spot on the ground to get a good spot to watch, that’s what he was here for anyways.

“Oh, stars brother you are so rude!” Papyrus looked like he was giving a pout and Sans let a raspy chuckle escape him at the display, he missed how Undyne tensed just the slightest bit at the sound since he was so focused so much on Papyrus.

“sorry bro, still _bone_ tired.” Gosh that one was so weak he really was exhausted if he couldn’t get his brain to function correctly to come up with a good pun, Papyrus seemed to notice as he gave him a very unamused look, shocked at the lack of effort in one of the few things Sans adored.

Shaking his head Papyrus went to speaking with Undyne, probably discussing on what they were going to do in the sparring session today. Sans just leaned back and waited for it to start, while he was tired he would love to see his brother in action and see how much he had improved, while he may be more adoring than necessary and blew up his brother’s ego way more than necessary he had no doubt Papyrus could be a great fighter.

“ALRIGHT NERD! LET’S GET STARTED!”

 

 

The session had lasted for about 2 hours and while Sans was honestly amazed at the skills his brother displayed he was extremely tired and grumpy now. All he wanted to do was to crawl back into bed, but he even had work today once Papyrus was done here, though it was worth it to see Papyrus’ true skill show.

When Papyrus turned and looked at Sans with that expectant look he melted a little on the inside, Papyrus was always so eager to please and he always wanted my approval and it did funny things to his insides.

“papyrus that was amazing! I never knew you could fight so well, you’ll definitely be in the guard in no time!” The sunshine look Papyrus gave me it worth it, Sans stood up from his spot on the ground and dusted himself off and gave a long stretch, the further he could get away from Undyne the better, she was just way too energetic for his tastes.

“Man, Papyrus you’re getting stronger and stronger! Let’s go inside for some tea!” With that Papyrus grabbed Sans’ hand and they all walked into her home, he was really hoping to just go home but he didn’t want to upset his brother with his sour mood.

 

Papyrus and Undyne were chatting pretty loudly out of their battle gear, while Sans just rested his head in his palm waiting for them to finish up, he had already finished the Golden Flower Tea she had provided and was just patiently waiting for them to be done with talking about whatever they were talking about.

“OH, STARS! I AM GOING TO BE LATE FOR MY PATROL!” Papyrus’ voice spiked so loud in volume Sans almost fell out of his chair. He was hardly able to register what he was doing until he heard the crashing of glass and suddenly Papyrus was gone, he had jumped out the window.

His brother was certainly unique.

“well, that’s my cue to get on out of here…” Sans stood up and stretched as he made his way to the door. Something in his soul sent a jolt of fear and the whipping of something in the air caught his attention, just in time he side stepped and saw one of Undyne’s spears nailed into the ground right where he was.

“Heh, I guess you do have some natural battle instincts in you, lazybones! Stay on your guard always!” Undyne didn’t know what it was about Sans but she always felt he had some hidden strength under his extremely calm demeanor, while he always seemed to be lazing around there was a certain confidence in him that she recognized, and to be honest how he was always so calm was pissing her off.

“undyne…” his voice was low and gravelly, a warning tone, the eye lights in his sockets vanished and Undyne was almost floored by the chilling look he was giving her but she was the Captain of the Royal Guard and she would never back down from a challenge! She wanted to see what this skeleton had in him!

“undyne I am warning you, if you take another step towards me you’re really going to regret what happens next.” Undyne was never a good listener and she wanted to push him, to see what he would do and see what he can do.

“As if I would back away from a challenge! NGGAAAHH!!!” She let out her battle cry as she threw another spear forward and attempted to lunge at him, to her surprise he backflipped out of the way and was immediately on his toes, she was actually extremely caught off guard by this and wasn’t prepared when he suddenly grabbed her arm and twisted it, slamming her into the ground.

“AGH! What the fuck you’re strong!” Undyne strongly with his iron grip and heavy weight, this was _nothing_ she expected, a growl made it way through her chest and she was able to throw Sans off with her legs and he stumbled back, she took the opportunity to try and lunge and punch him but he was much quicker, sidestepping and sweeping Undyne’s legs from under her. She winced when her head smacked onto the ground of her floor.

When she opened her eyes Sans was getting closer to her and she threw her hips out locking her legs around his femurs and twisted which caused him to fall onto the ground, he let out a grunt and hiss as he fell hard onto his back and Undyne took the opportunity to pin him.

But he wasn't going down, and Undyne loved it, this was getting her excited even, that look in his eyes was serious and he was harder to take down than his brother!

She again was caught off guard in the midst of her admiration and Sans used his legs to wrap around her waist and threw her with surprising strength off of him, so much so she crashed up right into the wall on the other side of her home, the wind had completely been knocked out of her. She opened her eyes in shock when her arms were shoved so hard into the wall it felt like something had cracked in her, Sans was giving her the most intense look she had seen in her life.

He looked genuinely angry and she could hear a subtle growling coming from his chest and his teeth seemed to be grinding against one another, she thought they were always glued together but upon closer inspection, he had uniformed fangs on the sides that were becoming more prominent in his anger.

She didn’t realize the shuddering breath that came from her when he had pinned her against the wall, there was something about this that was doing it for her, she never even found herself really looking at Sans that way but now that she looked he was a pretty good looking dude and this strength of his was really riling her up!

“obviously you need someone to knock you down a peg, you aren’t going to overpower me undyne.” She couldn’t stop the shiver and she felt herself wilting under that look he was giving her, _stars that look_.

Sans was smirking at her reaction and leaned forward and pressed his leg between her, she tried to squirm away from the pressure but he held strong and Undyne felt a heavy breath leave her as he ground his leg right against her core, he almost seemed to know exactly where to pinpoint too as if he had this hundreds of times before.

Undyne shivered when Sans lowered his skull down to her neck and she got a glimpse at those fangs that seemed a lot longer than she originally thought and a serpentine glowing, slimy blue tongue made of his magic slithered out of his mouth, it was only a small-time window of viewing before he latched onto her neck and pain and pleasure bolted up her body, His tongue was slithering over her, and it was causing sparks of intense cold pleasure to fill her up. She didn’t even realize she was moaning loudly until he gave her smug look.

She also didn’t realize she had begun grinding against his leg in the lapse of temporary control she had with herself. She tried to push him off even though she _really_ didn’t want this to stop oddly, she never had anyone show this much power over her and it was addicting, intoxicating. This was further emphasized when he grew aggravated with her struggling and slammed her against the wall again, pinning her wrists above her head with one hand and wrapping his hand around her throat with the other.

“NGH! F-fuck Sans!” She felt herself blushing horribly with the incredibly confident and smug look that overtook his features, she hadn’t meant to let that slip out but he was making her feel way too good and she was quickly falling victim to his strength.

“so this is how to cool you down, heh, you’re pretty cute like this ya know?” Undyne didn’t catch the whimper she let out and he looked absolutely wolfish at the response, he had no idea that Undyne would crumble like this under him and it was giving him a power high that he didn’t know he’d enjoy so much.

Deciding to get more adventurous he allowed his hand to squeeze around her neck tightly before letting go and watch as her pupils dilated in response, so she liked that?

Undyne squeaked when she felt his hand glide down her collarbone and ghosted around the area of her breasts, the sharp points of his phalanges scratched her scales and skin pleasantly and she bit her lip in response to prevent letting out any more embarrassing noises. She was a lot easier to touch without all that armor, she had gotten out her armor after Papyrus and her had finished training, and her nipples were poking through her tank top and she wanted to hide her face in shame.

She gasped when he grabbed her jaw and forced her to look into his eyes, the expression was so smoldering and lustful she shook on the spot, arousal pooling heavily between her legs in response. There was a brief look of shock that passed his features but he quickly covered it up and jutted his leg up harshly and Undyne let out a cry at the burst of pleasure.

“H-hah…Sans…heh…I didn’t know you had this side of you…” She gave a lopsided grin and he responded with an odd look, one that looked rather disapproving.

“you’re still coherent…let’s see if I can fix that.”

“Huh, AH!” Undyne yelled as he threw her on the floor, her chest and shoulders whined in protest at the pain and before she could sit up she felt Sans on top of her grinding into her rear as he leaned forward pressing his ribcage into her back, Undyne groaned at the heavy weight on her but then moaned as she felt something pressing hard against her rear and it _wasn’t_ bone.

“Heh…you think that puny thing can get me riled up hu-AH!” She yelled again when he harshly slapped her rear and it sent her forward a bit from the force, she was ashamed to admit it but she enjoyed that a little _too_ much.

“well if you think it’s so puny then surely you can take it without any prep huh _Undyne_.” He was growling consistently now and she was practically shivering underneath him, something about the primal way he was acting and his dominance over her was going to make her burst at the seams.

A gasp of shock left her as she felt him ripping her jeans with his _bare hands_ around her pussy and she whimpered when the air hit it, she hadn’t realized how wet she was until now, _stars I’m practically dripping_.

“it’s like a fuckin’ _waterfall_ back here,” she groaned a little at the pun but was cut off when he pressed against her again, but something was definitely different! He had unzipped his jeans and pulled them down to allow his girthy cock out, Undyne looked over her shoulder for a peak and she really regretted that comment about calling it puny, it was average in length but that girth was something to be scared of, she had never seen someone so wide before.

“you’re pretty freaky Undyne, getting off to being manhandled like this, who woulda thought the captain was such a masochist _huh?”_ Undyne let out a drawn-out moan when he reached down and pinched her clit and she almost came from that along with his dirty talk, why was he affecting her so strongly?

“Rrrgggh, shut the hell up Sans! I swear to Asgore if- HAAH!” She let out a loud moan when he suddenly shoved in and she immediately felt the burn and stretch, he was so _big_ and stretched her so much she could almost feel herself drooling, she went a bit lax on the ground as he stilled in a surprising act of mercy. Though she could tell he was admiring how his dick had shut her up instantly and how she was squeezing around him.

“hmm, you’re gonna cum already? some stamina ya got captain, you better not cum until I say so.” While Undyne wanted to tell Sans to fuck off and that he couldn’t tell her what to do she felt this odd inclination to obey, she was always bossing people around but she realized she loved actually giving control to someone else, especially someone obviously much stronger than her.

“mmm, _beg_ , I know you want me to fuck you, I can feel how your pussy is clenching around me, so _fucking beg_.” She grounded her teeth and clawed into her floor as she tried to control muscles in her pussy to stop trying to pull him in so much, but she couldn’t help the way her heart pounded and how much she actually _wanted_ to beg for him.

“i’m waiting…” he let out in a sing-song voice, refusing to even touch her now.

“F-fuck, o-okay, S-sans, please, oh stars please fuck me your cock feels so good, I want it so badly, Sans fuck me please!” She almost felt like fainting from the amount of heat in her face, but by the gravelly chuckle Sans let out he was satisfied, she moaned lowly when he leaned forward and wrapped his arms around her waist and brought his skull close to her ear, she could hear and feel how heavily he was breathing and his scent was all around her.

She started practically screaming when he began a deep and hard pace in her and it took every ounce of her willpower to not cum like he said so, it was so hard though! The essence his dick was made of made everything tingle within her not to mention the drag and pull it had on her walls and how it stretched her, _oh god he’s fucking good_.

“H-haaah! FUCK! Sans please I’m going to cum!” She wouldn’t be able to hold out much longer regardless of what he said, he was just fucking her too good, especially now that he was speeding up, there was so much fluid from how wet she had gotten that she could feel a distinct sticking sensation whenever his pelvic bone smashed into her ass.

“ _don’t you fucking dare!”_ she almost let out a wail in pain but it was cut short when he wrapped his hands around her neck and begun pounding into her like his life depending on it, with the deprived air, she grabbed his hands and garbled moans left her mouth as tears ran down her face and drool seeped out her lips, she couldn’t even think straight anymore, nothing but sounds of pleasure leaving her mouth.

She was about to feel herself faint, whether it be the lack of air or pleasure she was definitely blacking out, he needed to hurry up!

“mmmfff, fuck you feel so good undyne…” his breathing was becoming more haggard and stars were bursting in her eyes as he started slamming even harder into her. She felt her liquids squirt all over his jeans and he kept fucking her through it all.

She felt so submissive to him it was overwhelming her mind, she was his for him to do what he wanted and all of this power he had just made her natural instincts kick in, she wanted him to fill her up, _wait no!_

“Sans… don’t…. cum inside… me…” She garbled out roughly around the tight grip on her neck, though she heard a grunt of approval and clenched her jaw when he kept fucking her through her orgasm, that eventually caused her to faint.

Sans roared when suddenly Undyne’s pussy had squeezed him like a vice and let go of her neck to avoid crushing it as he clenched his jaw so hard it thought it might crack, he had heard her request and pulled out just in time to furiously jack his member as he sprayed his load all over her back.

When he calmed down from the intense orgasm he realized that Undyne wasn’t moving, she had fainted and Sans looked down at her with a smirk, though not being too cruel he went to the sink and grabbed her a glass of water and sat on the floor with her, bring her head into his lap as he waited for her to come to.

It wasn’t too long before Undyne groggily opened her eyes and saw Sans looking down at her with a smug expression, she immediately turned red and looked away, only to wince when he roughly snatched her chin and forced the glass of water to her lips.

“drink.” She nodded obediently and greedily drunk the water feeling a lot better almost immediately. When she finished, she realized Sans was still looking at her with that smug look in his eyes and she tried to look away again, he had been combing through her hair with his fingers but yanked tight when she tried to look away again.

“W-what?!” She squawked, she couldn’t keep looking at him when he was like this, it was doing weird things to her soul.

“why’d you want me to pull out hmmm?” he almost looked like he knew the answer, but he probably just wanted to hear it out of her mouth just to see her embarrassed further.

“I-I…Sans…” Undyne was shocked by the whine that left her mouth, she was shocked that he was still affecting her so strongly.

“You were driving me crazy…and…I wanted…oh for fuck sake don’t make me say it!” Undyne shoved him but she forgot how weak her body was from him fucking her so roughly and squeaked when he pinned her swiftly, the look in his eyes was predatory.

“ya wanted me to breed you, was that it?” Even with her head clear she couldn’t help the very violent jolt that shook her body very visibly to him, she wanted to bash her head into the wall and not stop until it was gone, why wasn’t her body listening to her but him?!

She only nodded, way too embarrassed to speak it out loud, she shuddered violently when he traced his phalanges down to her stomach and where it remained, the look in his eyes was turning primal and she had to will everything to push back against him gently.

“H-hey…that’s enough of that big guy…” she smiled meekly at him and he seemed to snap out of his daze and looked at her in wonder before smiling back and getting up, sweeping her up into his arms, she cried out in retaliation but she knew already he wasn’t going to put her down, he showed just how he wasn’t going to let her have her way already.

“i think you can take the day off today captain, rest up.” Sans walked into her bedroom and placed her on the bed, she blushed hard when he pressed his now closed teeth to her forehead in what was she presumed a kiss, it was the same but it felt oddly intimate, then she wanted to pull him back, they hadn’t kissed at all during all of that.

So, she pulled him down by the denim jacket he was wearing, which made him look all that more attractive and kissed him on his mouth, though she wasn't expecting the morphing to lips as he kissed back and when he wormed that tongue of his into her mouth, quickly dominating the kiss leaving her breathless.

“C-can…Can we do that again sometimes maybe?” She looked sheepish, just what was she asking? To be fuck buddies with Sans of all people? She couldn’t help it though he was… _really_ good…and just the type of thing she needed to get the stress out of her body, plus he was also rather sexy looking at him now, knowing the power he held in his stance, all of that screamed sex appeal to her.

“sure thing baby.” She jolted at the pet name and was going to yell at him but when she looked he was gone, wasn’t even near the house, she couldn’t feel any of his magic anywhere and she threw her face down into her pillow and screamed, she felt like she was quickly developing a crush on him from how he was treating her, she never thought she’d fall victim to the mysterious, somewhat bad boy type character but man he had proven her wrong.

She turned onto her back and stared at her ceiling, just thinking of all the things she just learned about herself, and how she was shocked about being into all of that, and the most important thing on her mind was.

She really wished Papyrus had brought Sans over to watch him train _much_ sooner.

                                                                             

 

 

 

 

**Author's Note:**

> Just to clarify why Sans was teaching Undyne so much about the cumming inside her thing is due to the fact in the context of how i write my stories, Monsters can't get pregnant unless they desire kids and want to become Pregnant, which is why Undyne panicked when she felt that instinctual feeling washing over her. Though it only happened because of how overwhelmed Sans was making her feel and he was proud of that and it's why he teased her about it, though he himself had a bit of trouble controlling himself as shown when he was staring at her stomach. 
> 
> What would be the kink for someone who was attracted to strength and power? Cause whatever that term is that's what Undyne is for sure here.
> 
> Even though canonically Undyne is with Alphys I have a feeling that she would love something like Power play and I feel like only someone like Sans or Asgore could truly do that without stopping, questionable with Asgore but Sans I feel like for sure. Power play is my shit and I'm sure Undyne would be hella into it too!
> 
> Follow me on Tumblr!
> 
> cryosintiger.tumblr.com


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